Even though they have yet to be discovered, let's say for the sake of argument that gravitons exist. And let's also assume that, like other particles, graviton symmetry also exists, giving anti-gravitons. Since for other particles, their antiparticles exhibit opposite charges and spins. In the case of gravitons, this would equate to an 'opposite force,' in this case a repulsive force instead of the attractive force propagated by the more common graviton.

So my question is, could anti-gravitons be responsible for 'dark energy' that is resisting being uncovered? And if so, could the production of anti-gravitons be in ascendance throughout the universe over time via a process that is currently not understood?